Category: Silica Refractories

Methods of Increasing the Service Life of Silica Bricks in Glass Melting Furnaces

KilnRefractory

Traditional and new refractory materials are used for glass kiln construction and repair. Traditional refractory materials for industrial use include clay bricks, dense clay bricks, mullite silica bricks, mullite bricks, mullite corundum bricks, and corundum bricks. High-temperature insulation materials and high-purity magnesium spinel refractory materials. Unshaped refractories include plasticized aluminum silicate cement, high-alumina cement, and low-cement castables.

Silica Bricks for the Glass Kiln
Silica Bricks for the Glass Kiln

The use of refractory materials in glass melting furnaces. Silica bricks are widely used in glass melting furnaces, and the main component is silicon dioxide (SiO₂). The silica brick used in the glass melting furnace requires a SiO₂ content of 94% or more, a maximum operating temperature of about 1600~1650℃, and a density of 1.8~1.95g/cm³. The apparent porosity is required to be less than 22%. The larger the porosity, the worse the quality of the silica brick. The appearance of silica bricks is mostly white crystals, and the microscopic composition is tridymite crystals. Because silicon bricks undergo crystallization conversion and volume expansion at high temperatures, especially at 180~270℃ and 573℃, the crystallization conversion becomes more intense. Therefore, in the process of the baking kiln and cold repair, it is necessary to adapt to the crystal transformation of silica bricks and take appropriate measures such as elastic strips. The silicon brick masonry should be left with expansion joints.

Rongsheng Silica Bricks for Sale
Rongsheng Silica Bricks for Sale

How to Improve the Performance of Silica Brick in a Glass Kiln

The advantages of siliceous materials are high-temperature strength, good creep resistance, low density, no pollution to glass, and low price. The working temperature of silica bricks is about 200℃ higher than that of clay bricks, but the corrosion resistance to molten glass and alkaline flying materials is poor. Therefore, it is used for masonry structures such as masonry, parapets, and small furnaces. When masonry, use high-silicon refractory mud or silica brick powder and other materials close to the composition of silica bricks as the cementing material.

RS High-Quality Silica Bricks
RS High-Quality Silica Bricks

Ways to Improve the Life of Silica Bricks

In the 1980s, my country introduced advanced silicon brick manufacturing technology for glass kilns from the United States. In order to distinguish it from the original product, the product manufactured with imported technology is called high-quality silica brick. The composition (W) of high-quality silica bricks is cristobalite 45%, phosphorite 50%, glass phase 1%~2%, and a small amount of residual quartz. Melt index (2R2O+Al2O3)<0.5%.

After adopting oxy-fuel combustion technology, the life of silica bricks has been drastically reduced from 5 to 10 years to 2 to 3 years. Rat holes and erosion are the main causes of damage. The rat-hole is caused by the alkali in the gas leaking from the kiln condensing in the cracks of the brick to corrode the silica brick. The methods to improve the life of silica bricks are as follows:

  • 1) Improve the dimensional accuracy of bricks. Control size tolerance <0.5mm, brick gap width <1.5mm. The cracks between the bricks are narrowed, the kiln gas leaks less, the erosion is light, and the mouse hole is also small.
  • 2) Reasonably design the kiln lining structure. Move the condensation temperature zone of the alkali to the sealing layer behind the silica brick.
  • 3) Use low-calcium silica bricks with good corrosion resistance (w(CaO)≈0.8%). Figure 4 shows the corrosion resistance test results of low-calcium silica bricks and high-quality silica bricks. It can be seen from Figure 1 that when the alkali vapor pressure is low, the corrosion resistance of low-calcium silica bricks is better than that of high-quality silica bricks.
Cheap Silica Refractory Brick for Sale
Cheap Silica Refractory Brick for Sale

The influence of alumina content on the performance of silica brick for glass kiln

The increase of Al2O3 content is unfavorable to the refractoriness, softening temperature under load, true density, and mineral composition of the product. But it has no obvious influence on the apparent porosity, residual line change, and creep rate.

Development of High-Purity, Corrosion-Resistant Glass Kiln Silica Brick

China’s glass output has ranked first in the world. The main task for the future development of refractory materials for glass kilns is to improve the design, masonry, and maintenance of the kiln, reduce the adverse effects on the quality of glass, and extend the service life of the glass kiln. Silica brick is the main refractory material in the masonry of the glass furnace and is mainly used for the ceiling, hanging wall, and front and back walls of the glass furnace. To increase the service life of glass furnaces, higher requirements must be put forward on the quality of silica bricks. Therefore, the study of high-quality silica bricks for glass kilns with high purity and corrosion resistance can extend the service life of glass kilns to a certain extent.

RS Refractory Bricks Factory
RS Refractory Bricks Factory

Rongsheng Refractory Brick Manufacturer

Rongsheng refractory brick manufacturer is an experienced refractory material manufacturer and sales manufacturer. Rongsheng’s refractory products have been sold to more than 60 countries and regions all over the world. For example, Russia, South Africa, Kazakhstan, Philippines, Chile, Malaysia, Uzbekistan, Indonesia, Vietnam, Kuwait, Turkey, Zambia, Peru, Mexico, Qatar, etc. Obtain high-quality refractory products for glass kilns, such as AZS bricks, silica bricks, fused corundum bricks, checker bricks for regenerators, etc. Please contact us, we will provide you with services according to your specific needs.

Detailed Explanation of Semi Silica Refractories

KilnRefractory

Semi-Silica Refractories generally use silica as the main component and a glassy matrix as a binder. The silica content is about 75% to 93%. The raw materials are silicon-containing clay, sand and refractory mortar. According to the Kiln Refractories Blog, it can resist slag erosion and is used in open hearth furnaces.

Semi Silica Refractory Bricks
Semi Silica Refractory Bricks

Brief Introduction of Semi-Silica Refractories

The Semi-Silica Refractories have an A12O3 mass fraction less than 30% and a SiO2 mass fraction greater than 65%. It is a kind of refractory material that is made of wax stone, siliceous clay or primary kaolin and its tailings, coal gangue and other main raw materials, combined with clay as a binder.

Whether in China or international standards, there is no definition of Semi-Silica Refractories. However, refractory materials with a SiO2 mass fraction greater than 85% and less than 93% are defined as silica refractory materials. It also defines Al2O3, aluminum-silica refractories with a mass fraction of 30% to 48% as clay refractories. Traditionally, aluminum-silicon refractory materials with Al2O3 mass fraction between 15% and 30% are called semi-silica refractory materials. The crystal phases are cristobalite, mullite, and a certain number of glass phases. Its typical representative is wax stone brick.

Semi-Silica Refractories
Semi-Silica Refractories

  1. Raw Material of Wax Stone

The most commonly used raw material for producing semi-silica refractory materials is wax stone. The wax stone mine is composed of pyrophyllite, quartz, kaolinite, mica and so on. The ore is dense and massive, with a waxy luster. Different colors due to different impurities, such as gray, wax yellow, light brown, meat red, etc. It has a greasy feel, very similar to talc. China is rich in waxstone resources, mainly distributed in the volcanic rock development area on the southeast coast, of which there are many mining sites in Fujian and Zhejiang.

1.1 Chemical mineral composition of pyrophyllite

Pyrophyllite is a water-containing silicate mineral. In theory, A2O3 accounts for 28.3%, SiO2 accounts for 66.7%, and H2O accounts for 5%. A complex layered structure is formed by two layers of hexagonal silicon-oxygen tetrahedral mesh layer sandwiched by a layer of “aluminum hydroxide” octahedron (aluminum oxyhedron). Pyrophyllite is also known as Qingtian stone, Shoushan stone, seal stone, wax stone, etc. Can be divided into pyrophyllite wax stone, siliceous wax stone, kaolinite wax stone and diaspore wax stone. Often contains a certain amount of Fe2O3, CaO, R2O and other impurities.

1.2 Basic properties of wax stone

Due to the different mineral composition of wax stone, their differential heat curves are obviously different, and there are different endothermic and exothermic peaks. It can be seen that the sample will expand in a certain temperature range before being sintered. The reason is that the lattice expands and the aluminum oxide and silicon oxide layers are separated. Vigorous expansion began at about 700 ° C, dimensional changes at 900 ° C tended to be gentle, and 1100 ° C began to shrink. This expansion characteristic is the basis for the wax brick’s micro-expansion characteristic. Raw wax stone has very low hardness and is a commonly used engraving material, but its hardness and strength have been greatly improved after calcination. In addition, pyrophyllite has good chemical stability and can only be decomposed by sulfuric acid at high temperature.

  1. Key points of production process of semi-silica brick

The manufacturing process of semi-silica brick is basically similar to that of clay bricks. The biggest difference is that semi-silica bricks can be made of raw materials. The main points of its production process are as follows.

(1) When using natural silica clay and wax stone, it is necessary to decide whether to add clinker according to the nature of the raw material and the use conditions of the finished product. Raw materials can be used to make bricks directly. It is also possible to add part of the wax stone raw materials to the mature materials after calcination, or add% to 20% of clay clinker to replace natural silica clay.

(2) If quartz sand or silica is added as barren material, the particle size should be determined according to the product performance requirements. In general, if there are many raw material impurities and fine quartz particles, the fire resistance of the resulting product is low, the thermal shock stability is reduced, but the strength is increased. If the quartz particles used are large, the strength of the product is low, but the thermal shock resistance is enhanced and the load softening temperature is increased.

(3) The water content of raw wax stone is small (less than 7%). When the whole wax stone or a small amount of combined clay ingredients are added, the mud water is low and the bonding performance is poor. At the same time, in the process of using wax stone bricks, it is generally subjected to repeated heating and cooling, the expansion amount gradually increases, and the bulk density further decreases. Therefore, high-pressure molding should be used, generally the molding pressure is above 50 MPa. Some molding pressure is 50 ~ 100 MPa, or use vacuum degassing brick machine to mold high-density wax stone brick with high volume stability. This wax stone brick has small air permeability and small pore diameter, which can improve durability.

(4) The maximum firing temperature varies with the characteristics of the raw materials used. Low temperature firing is usually used, and the temperature is 150 ℃ lower than that of clay bricks with lower firing temperature, and generally does not exceed 1200 ℃. Cool slowly after firing.

  1. Performance characteristics and application of semi-silica brick

The semi-silica brick produced with pyrophyllite as the main raw material has a refractoriness greater than 1700 ° C. It does not shrink at high temperature but has a slight expansion. It has good thermal shock resistance, can withstand the impact of steel slag and metal, and has strong creep resistance. Its micro-expansion is conducive to improving the integrity of the masonry and weakening the erosion of slag on the masonry along the brick joints. At the same time, glaze-like substances with high viscosity can be formed on the surface of semi-silica  bricks during high-temperature use to prevent the penetration of slag into the bricks, thereby improving the ability to resist erosion of the slag. In order to improve the performance of semi-siliceous bricks, it is sometimes necessary to add some other substances, such as adding mullite, high-alumina clinker, and zircon to increase the heat resistance of refractory bricks.

Semi-silica bricks are mainly used for ladle bottom lining, ladle lining, pouring steel bricks and kiln flue. With the increasing requirements for steel quality, the amount of semi-silicon bricks used in the steel industry has been very small. In addition to wax stone, other semi-silicon materials and minerals can also be used to make semi-silicon refractory materials.